20 Jan

Auto-populating Select Boxes using jQuery & AJAX

Update: due to popular demand, I've caved in, and written a plugin and demos with multiple-select boxes populating each other and driven from MySQL.

View: Auto-populate multiple select boxes

If you are familiar with using select boxes for categorisation and sub-categories, such as ebay does when selling an item, usually this can require a lot of JavaScript to maintain the select boxes, but jQuery can hugely simplify this task by adding a dash of AJAX.

The Goal

Allow the user to select a top level category from one select box and to automatically populate the sub-category.

Prerequisites

Latest copy of jQuery
A basic understanding of JSON (don’t let this put you off - it’s really very, very easy)
A server-side script that can respond to the AJAX request (though I’ve provided a simple example)

Demo

Our demo will specifically look to build a simple form that allows us to book human resource for a project. The top level category is the resource type, and the sub-category will list the individual’s names.

See the demo in action

How it works

Once the top level category select is changed, it sends an AJAX request for the sub-categories. The result of which are converted to select options and the sub-category select’s elements are replaced.

Unobtrusive JavaScript

First things first: as with any page that is loaded with JavaScript and AJAX functionality, it should work without JavaScript.

To achieve this for our tutorial here’s what we need to ensure:

When the page is loaded, the sub-category is loaded (if the top level has a selected item).
There is a ‘load sub-category’ button the user can select to re-load the page. We will hide this button with a <noscript> tag in our demo.

The Code

There are 4 parts to this demo.

The page’s HTML.
The server-side code to produce the dynamic page (i.e. to pre-load the select boxes when the user first visits).
The jQuery & JavaScript.
The JSON response (which will reuse the server-side code).

HTML

<form action="/select_demo.php">
  <label for="ctlJob">Job Function:</label>
  <select name="id" id="ctlJob">
    <option value="1">Managers</option>
    <option value="2">Team Leaders</option>
    <option value="3">Developers</option>
  </select>
  <noscript>
    <input type="submit" name="action" value="Load Individuals" />
  </noscript>
  <label for="ctlPerson">Individual:</label>
  <select name="person_id" id="ctlPerson">
    <option value="1">Mark P</option>
    <option value="2">Andy Y</option>
    <option value="3">Richard B</option>
  </select>
<input type="submit" name="action" value="Book" />
</form>

Server-side

This is just a simple example, but it should be obvious that you can expand this to go off to a database and return an object in a JSON data structure:

<?php
if ($_GET['id'] == 1) {
  echo <<<HERE_DOC
[ {optionValue: 0, optionDisplay: 'Mark'}, {optionValue:1, optionDisplay: 'Andy'}, {optionValue:2, optionDisplay: 'Richard'}]
HERE_DOC;
} else if ($_GET['id'] == 2) {
  echo <<<HERE_DOC
[{optionValue:10, optionDisplay: 'Remy'}, {optionValue:11, optionDisplay: 'Arif'}, {optionValue:12, optionDisplay: 'JC'}]
HERE_DOC;
} else if ($_GET['id'] == 3) {
  echo <<<HERE_DOC
[{optionValue:20, optionDisplay: 'Aidan'}, {optionValue:21, optionDisplay:'Russell'}]
HERE_DOC;
}?>

Note that this is not accessible. To ensure accessibility, the server side will handle the pre-population of the select boxes as the page is loaded. Here is an example (excluding the headers, footers and JavaScript) of the accessible example.

JSON Response

If I pass the server side id = 2, i.e. /select.php?id=2&ajax=true, the return value is (the ajax=true is an arbitrary flag that I’m using to differentiate between a normal user request and one done via AJAX):

[ {optionValue:10, optionDisplay: 'Remy'},
{optionValue:11, optionDisplay: 'Arif'},
{optionValue:12, optionDisplay: 'JC'}]

The enclosing square brackets denotes an array and each element is separated by a comma.

Within the array are three objects. If you’re familiar with PHP or Perl, you can basically treat these as hashes. The objects have keys (in this case two keys, one called ‘optionValue’ and one called ‘optionDisplay’), and values. Note that keys don’t need to be wrapped in quotes (though in some cases you will need them sometimes).

There are two ways which we can get the data out of this structure (assuming j is the structure):

alert(j['optionDisplay'])

Or:

alert(j.optionDisplay)

jQuery & AJAX Request

Our JavaScript is going to attach itself after the page is load, and fire an event each time the job function select box is changed.

The event will send the new value of the select box and reload the contents of the person select box.

Note that I’m be a bit naughty here, in that I’m plugging HTML directly in to the DOM.

Each item in the JSON response is looped round and used to build up the new options for the select box. As the response is an array (as mentioned earlier), we can call the .length method on it.

<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" charset="utf-8">
$(function(){
  $("select#ctlJob").change(function(){
    $.getJSON("/select.php",{id: $(this).val(), ajax: 'true'}, function(j){
      var options = '';
      for (var i = 0; i < j.length; i++) {
        options += '<option value="' + j[i].optionValue + '">' + j[i].optionDisplay + '</option>';
      }
      $("select#ctlPerson").html(options);
    })
  })
})
</script>

Where to take it next

So that’s the primer. Next steps: upgrade, integrate, extend and stylise. Below is an example of the category selection when submitting an item for sale on Ebay.

Ebay Category Selection

It should be a simple next step to integrate a database behind the selection methods and create more complicated selection like this Ebay example.

Let me know if you spot any glaring errors or have any comments.

You should follow me on Twitter here I'll tweet about JavaScript, HTML 5 and other such gems (amongst usual tweet-splurges)

160 Responses to “Auto-populating Select Boxes using jQuery & AJAX”

Stephen Cassady May 15th, 2007 at 6:44 am

Thank you!
Now, I've got 3 select boxes, the first changes the second, the second the third. What I would like, is when the first is changed again, the third is removed or reset to a empty selector (hidden is fine, I'll qaqc after the submit to ensure that all three do parent-child chain). Anyway, what can I change in the JQuery (example code below) to chain the hiding of the of the last select box (#city)?

Thank you again.

$(function(){
$('#country').selectCombo('index.cfm?fuseaction=_ajax.return_plprov', '#prov');
$('#prov').selectCombo('index.cfm?fuseaction=_ajax.return_plcity', '#city');
});
Lance May 19th, 2007 at 5:17 am

Hi,
I’m new to all of this and am having trouble getting your code to work for some reason. Could you please make a zipped working example package for download that includes a separate JSON data file?
I somehow need to make a chain of 3 select boxes that use the value/key of a selected option (not the text) to base the populating of the next select box with.

Thanks
Blog Author Remy Sharp May 20th, 2007 at 8:51 pm

@Guy - thanks for point out that bug in IE6 ::groan:: - IE6 really must do things it's own way! Though I would suggest a small change to the code so you don't have to rely on the timeout in the other browsers (though it could be improved to select IE6 downwards - but you get the picture):

$('#Test').html(optionstring); var selectFirst = function() { $('#Test option:first').attr('selected','selected'); }; $.browser.msie ? setTimeout(selectFirst,1) : selectFirst();

@Stephen - you need the following code change to empty the third select box when the first is selected (I'm not able to test it, but I'm fairly sure it should do the trick):

$('#country').selectCombo('index.cfm?fuseaction=_ajax.return_plprov', '#prov').change(function() { $('#city options').remove(); });

@Lance - I'll get back to you soon with a working example that you can download.

Hope that helps you all! Cheers for the feedback.
Stephen Cassady May 21st, 2007 at 3:52 am

@Remy - thank you for the code suggestion. I've tweaked it a bit, the "remove" removed the 3rd select completely, and it wouldn't come back even on change of the second select. I've used "hide" instead:
change(function(){$('#city').hide();})
and it works (hide the third choice, but it comes back on the selection of the second).

I want to say thank you - this is one of the first jquey items I've worked with, and I knew I wanted to chain things, just couldn't figure out what/how. You feedback not only helps with the specific example, but improves my understanding of chaining with jquery. Thank you.
J.B.C. June 5th, 2007 at 3:19 am

I can't seem to get this to work. I can't duplicate the example. I don't really understand how the html (with js) and php files work (i.e. I don't see where the php script is being called so I'm probably naming something wrong). Can you offer any help ?
Blog Author Remy Sharp June 8th, 2007 at 12:11 pm

@J.B.C - the key is in the getJSON call here:

$.getJSON("/select.php",{id: $(this).val(), ajax: 'true'}, function(j) { ...

This is the JS that makes the AJAX call to the select.php on your web server. The response is then fed in to the function that we also pass in to the getJSON method.
GB June 12th, 2007 at 7:59 pm

Is it possible to implement this without the use of a server side for testing purposes. Like just static json and output the entire 3 column select box? Also completely using the jquery library?
GB June 14th, 2007 at 1:04 am

Ok making it like the ebay with multiple selected does not work at all. Are you guys even sure that this works? I've been having trouble with how you all explain your changes. When I select from the first column, everything from the second column gets selected too. And it does not work for IE. For those who did get it working, can you provide the code you did?
Auto-populating Select Boxes with AJAX and MYSQL | TechRoam June 20th, 2007 at 5:23 pm

[...] the calls to the server. I found a couple examples that did something similar to what I needed but did not use a database, did not have third box functinality, or did not work in all browsers. I encountered a known [...]
Marco Antonio June 20th, 2007 at 8:25 pm

Very good Remy. Do you can share with us your know how to create a 3 related selects? Cheers.

support_republic_of_kosova July 9th, 2007 at 10:59 am

For people interested in using this tutorial with mysql
1. include your connection

include(connect.php);
$id = $_GET['id'];

choose a table

if(isset($id))
{
    switch ($id)
        {
        case 1:
        $tbl = "tabel 1";
        break;
        case 2:
        $tbl = "tabel 2";
        break;
        case 3:
        $tbl = "tabel 3";
        break;
        }
}
$q = mysql_query("select id, title from ".$tbl." order by title ASC"); //query
while($r = dbFetchAssoc($q))
{
    $id = $r['id'];
    $titel = $r['titel'];
    $str = "{optionValue:$id , optionDisplay: '$titel'},";
    $newstr .= $str;
}
$str = substr($newstr,'',-1); //remove last coma
echo <<DOC
[
$str
]
DOC;

Hope this will be useful to somebody

Jehzeel Laurente July 16th, 2007 at 7:59 am

wow great example! i love it, i'm gonna use it in my next web app.. hihihi.. thanks.. ^_^
Mike July 26th, 2007 at 4:21 am

would really like a full example that shows the database piece.
Uday August 3rd, 2007 at 11:28 am

Dear sir,
I want to use a text box for the user to type letters and query the database to get some results and populate in a list box. Is it possible to do that. like google doing it in browser toolbar.
Thanks,
Uday
Blog Author Remy Sharp August 5th, 2007 at 10:05 am

@Uday - I think what you're after is here:

http://bassistance.de/jquery-plugins/jquery-plugin-autocomplete/
Steve August 14th, 2007 at 9:11 pm

We too are having trouble getting it to work like ebay. Any suggestions? I am willing to donate for your time if we could get a working version.
Guy August 23rd, 2007 at 3:21 pm

Remy - thank you for the nice example. I was able to easily get it working using ColdFusion instead of PHP for a project I am working on. Always nice to have clear practical examples like this - thanks!
youshrin September 18th, 2007 at 11:14 am
thanks for the example!but i badly need help!
```
$(function(){
  $("select#ctlJob").change(function(){
    $.getJSON("/select.php",{id: $(this).val(), ajax: 'true'}, function(j){
      var options = '';
      for (var i = 0; i < j.length; i++) {
        options += '' + j[i].optionDisplay + '';
      }
      $("select#ctlPerson").html(options);
    })
  })
})
```
suppose i need to send more than 1 id in the function,how can this be done!
$.getJSON("/select.php",{id: $(this).val(), i need to send 1 more id here to form a url based on these two id: $(this).val(), ,ajax: 'true'}, function(j){
Blog Author Remy Sharp September 18th, 2007 at 11:31 am
@youshrin - Without knowing more about the particular example, I would do this:
```
$.getJSON("/select.php", { id1 : $(this).val(), id2 : $('#select2').val() }, function (j) {
  // process
});
```
youshrin September 18th, 2007 at 1:19 pm

thank you very much!
it works!

remy sharp's b:log